Energy Dissipation in Magnetohydrodynamic Turbulence: Coherent Structures or "Nanoflares"?

TL;DR

This study explores how energy dissipates in MHD turbulence, revealing that it occurs in a continuum of thin, coherent structures across scales, supporting the nanoflare hypothesis for coronal heating.

Contribution

It provides new insights into the scale and distribution of dissipative structures in MHD turbulence, linking coherent structures and nanoflares.

Findings

Energy dissipation follows a power law with index near -2.0.

Dissipative structures are uniformly distributed in the inertial range.

Structures become thinner and more numerous with higher Reynolds numbers.

Abstract

We investigate the intermittency of energy dissipation in magnetohydrodynamic (MHD) turbulence by identifying dissipative structures and measuring their characteristic scales. We find that the probability distribution of energy dissipation rates exhibits a power law tail with index very close to the critical value of -2.0, which indicates that structures of all intensities contribute equally to energy dissipation. We find that energy dissipation is uniformly spread among coherent structures with lengths and widths in the inertial range. At the same time, these structures have thicknesses deep within the dissipative regime. As the Reynolds number is increased, structures become thinner and more numerous, while the energy dissipation continues to occur mainly in large-scale coherent structures. This implies that in the limit of high Reynolds number, energy dissipation occurs in thin, tightly packed current sheets which nevertheless span a continuum of scales up to the system size, exhibiting features of both coherent structures and nanoflares previously conjectured as a coronal heating mechanism.